As warm weather approaches, the warnings go out, serving as reminders about mosquito- and tick-borne illnesses. West Nile infection, Eastern Equine Encephalitis and Lyme disease are familiar threats to our health every year, and it’s important to heed the alerts.

This year, however, public health officials are raising additional alarms on two other fronts: the resurgence of vaccine-preventable illnesses and the introduction of infectious diseases from other countries.

Infectious diseases affect hundreds of millions of people worldwide every year. These illnesses are caused by viruses, bacteria and other pathogens that enter the body, commonly through skin contact, inhaling airborne particles or insect bites.

We are fortunate in the U.S. in that we have full-time public health professionals at the federal, state and local levels; medical professionals who specialize in infectious disease; state-of-the art sanitation methods; and a culture that values prevention, especially for our children.

We also have the protection of vaccines. Our high rates of immunization in the U.S. give us the benefit of "herd immunity" or "community immunity" – a form of immunity that develops when a large percentage of a population is immunized, thereby offering some protection to those who have not been vaccinated.

Despite our advanced public health programs and vaccines, the spread of infectious diseases in the U.S. is being pushed by two factors: global travel and a stubborn resistance to immunization.

The introduction into the U.S. of Middle East Respiratory Syndrome (MERS), which has claimed nearly 300 lives so far in the Middle East, is a reminder that global travel can carry diseases anywhere in the world and that infection - or an outbreak – can be just a plane ride away. A healthcare provider returning from the Middle East, where the viral, pneumonia-like disease originated, brought the illness into the U.S. in May.

Public health officials are also watching the spread of dengue and chikungunya, two other mosquito-borne viruses. Dengue, endemic to Puerto Rico, Latin America and Asia, infects 400 million a year and has been reported in Florida. Chikungunya, from Asia and Africa, is spreading quickly in the Western hemisphere, mostly in the Caribbean, where 25,000 cases have been reported, many at popular tourist spots.

We have seen the global spread of diseases before – bird flu, swine flu, and SARS (Severe Acute Respiratory Syndrome, a relative of MERS), the last of which reached four continents in 2003. The worrisome part about these diseases is that we don’t have specific treatments for them, and no vaccines exist for some of them. People with underlying health conditions who contract these illnesses could be affected with life-threatening complications.

A stubborn resistance to immunization, allowing for the return of vaccine-preventable diseases once thought eradicated in the U.S., is also raising concern. The number of measles cases in the U.S. this year has reached a 20-year high, with more than half affecting adults 20 and older. Many cases have been attributed to travelers. Similarly, outbreaks of mumps and whooping cough have occurred across the country. Even polio, eradicated long ago in the U.S. and on the brink of extinction globally just a few years ago, is returning in some countries.

Page 2 of 2 - Infectious diseases should merit everyone’s attention. Here’s what you can do.

Check on your immunizations, and get them up to date if needed. Talk with your physician, because even if you think you’re safe, you may need a booster shot for some conditions.

If you’re traveling overseas, a trip to a travel clinic is strongly advised, not only for vaccines, but also for food and water safety tips pertinent to the countries you’re visiting.

To guard against the threats of the mosquito- and tick-borne diseases, check household screens to keep out insects, eliminate standing water where mosquitoes breed, limit activity at dawn and dusk when mosquitoes are most active, wear long-sleeve shirts and trousers, and use an approved repellant. For added protection against tick-borne diseases, always perform a "tick-check" on yourself if you’ve been outdoors in the woods or near tall grass or shrubs.

Finally, remember that vaccination remains the best protection for many infectious diseases. The overwhelming scientific evidence shows them to be safe and effective, and if we take them as we should, we could prevent an enormous amount of disease.

For more information on infectious disease, travelers’ health and vaccination, including schedules for children and adults, visit the U.S. Centers for Disease Control and Prevention at www.cdc.gov. For a video discussion, visit www.physicianfocus.org/infectiousdisease.

George M. Abraham, M.D., M.P.H., an infectious disease specialist, is associate chief of medicine at Saint Vincent Hospital in Worcester, professor of Medicine at UMass Medical School and Massachusetts governor of the American College of Physicians. Physician Focus is a public service of the Massachusetts Medical Society. Readers should use their own judgment when seeking medical care and consult with their physician for treatment. Send comments to PhysicianFocus@mms.org.